Light Trapping by Means of Electric Field Enhancement in Metallic Gratings

The enhancement of the electromagnetic field within the grooves of a metallic diffraction grating is analyzed. A perfect conductor, rectangular-shaped diffraction grating is assumed, therefore, the field enhancement analyzed in this work is due to resonances caused by the structure itself, and not to the so-called surface-plasmon resonances which are observed to be influenced by metal properties as well. The modal approach has been employed for calculations. Basically, the squared amplitude of the electric field within the grooves is calculated as a function of the wavelength of the incident light. Similarly, the behaviour of the structure when exposed to a conical bundle of light is also analyzed. The present results show that a field intensity enhancement of the order of 100 is achievable. However, the spectral width of the resonances decrease with increasing enhancement as is expected